Digital televisions receive and display images that are broadcast as digital signals, for example as a stream of MPEG2 data. The digital televisions receive the digital signals on a digital medium, and place the MPEG2 data into a video buffer, much as a computer receives and stores video or graphics information.
Digital televisions may include many of the features of prior generations of analog televisions, including the ability to “zoom.” Zooming allows a person watching television to magnify a selected portion of the television screen. The selected portion is a “zoom frame.” The television displays the zoom frame, magnifying it to cover the entire screen, rather than the entire MPEG2 frames (i.e., the “full frames”) as received by the television.
Internally, the television defines the zoom frame in terms of its position and size within the full frame. Unfortunately, as persons and things move about the screen, they enter and leave the selected portion defined as the zoom frame. For example, if a the full frame belongs to a motion picture in which a person walks from the left edge of the screen to the right edge of the screen, the person will walk through the zoom frame. Panning of the camera exacerbates the problem. Panning is a cinematographic technique in which a cameraman pivots the camera to show a scene that is too large to be shown conveniently in a single frame. When a camera is panned, the image appears to slide from one edge of the full frame to the other edge of the full frame. Accordingly, unless the zoom portion is moved with respect to the full frame, the zoom portion includes images that slide from one edge of the zoom frame to the other.